Boosting oxygen evolution by nickel nitrate hydroxide with abundant grain boundaries via segregated high-valence molybdenum.

ABSTRACT

High-valence metal doping and abundant grain boundaries (GBs) have been proved to be effective strategies to promote the oxygen evolution reaction (OER). However, the reasonable design of the two to facilitate OER collaboratively is challenging. Herein, a convenient and novel one-step molten salt decomposition strategy is proposed to fabricate segregated-Mo doped nickle nitrate hydroxide with substantial GBs on MoNi foam (Mo-NNOH@MNF). When processed in molten salt, the Mo species on the conductive substrate migrates unevenly to the surface of Mo-NNOH@MNF, which not only induces the formation of abundant GBs to modulate electronic structure, but also improves the intrinsic activity as high-valence dopants, synergistically elevating OER activity. As verification, the optimized Mo-NNOH@MNF-10h exhibits low overpotential of 150 mV at 10 mA cm-2, which can be attributed to the reduced valence charge transition energy of Ni by high-valence Mo dopant, coupled with the fine-tuning of d-band center bond and corresponding local electron density by induced GBs and Mo doping, as DFT calculations revealed. Moreover, the intrinsic robustness and strong adhesion ensure the long-term stability of 6 h at 500 mA cm-2. This work provides a promising molten salt decomposition approach to synthesize advanced materials with unique structures.